1. Field of the Invention
The present invention relates to a liquid discharge head for performing such operation as to record or print characters, symbols, images, or the like, among some others, on a recording medium that includes paper, plastic sheet, cloths, commodity, or the like by discharging a functionating liquid, such as ink, to enable it to adhere thereto. for example. The invention also relates to a method of manufacture therefor, and a liquid discharge apparatus.
2. Related Background Art
As a liquid discharge head (ink jet recording head), there is the one that records images by bubbling ink to be discharged by utilization of thermal energy generated by heat generating members, for example.
Conventionally, as an ink jet recording head such as this, there is the ink jet recording head as shown in FIG. 9, for example, which is structured by mounting a ceiling plate 102, which is provided with an ink inlet port 103, a common liquid chamber 104, liquid flow paths 105, and discharge ports 107, on a base plate 101 having heat generating members 108 for bubbling use installed thereon for discharging ink.
For an ink jet recording head of the kind, various recording performances, such as image quality, resolution, and speed, among some others, are demanded to be higher still from now on. To materialize such higher recording performances, there is a need for structuring an ink jet recording head capable of discharging small ink liquid droplets with many numbers of discharge ports 107.
For the ink jet recording head of the kind, a method is adopted to simply make the area of a bubbling heat generating member smaller as the method to make a discharging ink droplet small in order to enhance the resolution. However, if the area of the heat generating member is made smaller, a desired bubbling cannot be obtained, because among the thermal energy generated by the heat generating member, the ratio of energy that may contribute to bubbling is caused to be gradually reduced. In order to generate a sufficient bubbling energy, it is necessary to set the area of heat generating member at a slightly larger value. If the area of the heat generating member is made larger, the dissipation of energy is increased inevitably. Also, if the area of the heat generating member is made smaller, a bubble itself becomes smaller to result in the reduced efficiency of bubble that should contribute to discharging. Also, if the arrangement density of nozzles is made higher in order to make a higher recording possible, the number of heat generating members should increase, while there is the incapability that the area of the heat generating member is made very small as described earlier. A problem is then encountered that the energy dissipation becomes greater.
In contrast, as the ink jet recording head capable of enhancing the energy efficiency by conducting the pressure exerted by bubbling to each discharge port efficiently, an ink jet recording head is disclosed in the specification of European Laid-Open Patent 0436047, which is provided with various kinds of valve mechanisms between the common liquid chamber and the heat generating member in the liquid flow path in order to cut off the liquid flow path when pressure is exerted by driving the heat generating member, and to permit the liquid flow at the time of refilling that necessitates the generation of ink flow from the common liquid chamber to each heat generating member after liquid has been discharged. This ink jet recording head is structured for the purpose of enhancing the energy efficiency by suppressing the escape of the pressure exerted by driving the heat generating member to the common liquid chamber side which is opposite to the discharge port, and conduct the pressure thus exerted to the discharge port side efficiently.
Also, as the ink jet recording head that discharges ink liquid droplets by enabling the pressure exerted by piezoelement to act on ink by utilization of the piezoelement which serves as an electromechanical converting member, there has been disclosed in the specification of U.S. Pat. No. 4,514,742, the ink jet recording head which is provided with various kinds of valve mechanisms between the ink replenishing path, through which ink is replenished to a pressure chamber, and the pressure chamber, which is provided with piezoelement for exerting pressure whereby to discharge ink, in order to cut off the liquid flow path when pressure is exerted by driving the piezoelement, and to permit the liquid flow at the time of refilling that necessitates the generation of ink flow from the ink supply path to the pressure chamber.
However, the valve mechanisms disclosed in the specification of European Laid-Open Patent 0436047 use a valve member the height of which is the same as that of the liquid flow path as the valve member that closes the liquid flow path, which moves in the condition where the valve member is in contact with the upper and lower faces of the flow path. As a result, when the valve member moves, friction occurs between the upper and lower faces of the flow path and the valve member to make it difficult to enable the valve member to move smoothly, hence making this arrangement impracticable.
Also, in the same specification, there is disclosed the structure in which a valve mechanism is arranged between the heat generating element and discharge port in addition to the one between the common liquid chamber and heat generating member. However, since this valve mechanism is structured so that the liquid flow path is closed in a steady state, the liquid flow is not allowed to occur unless a force is exerted to move the valve member. Therefore, although it is possible to refill liquid by moving the valve member by means of the difference between pressures exerted across the valve mechanism for the portion of the heat generating member where the pressure is reduced due to debubbling, there is a fear that liquid cannot be refilled sufficiently on the discharge port portion, because only the surface tension of liquid is the force usable for refilling liquid to the discharge port portion, which is not strong enough to serve the purpose.
Also, in the specification of U.S. Pat. No. 4,514,742 referred to earlier, the disclosed structure is such that the valve mechanism is formed by a valve seat configured as if to make a part of the liquid flow path narrower, and an elastically formed plate type valve member that cuts off the liquid flow path by being in close contact with the valve seat in a steady state where no ink flow occurs. This valve member is displaced by liquid flow when refilling so as to permit the liquid flow, but being biased to the valve seat side to cut off the liquid flow path in the steady state, the valve member needs a force to a certain extent to be deformed when refilling. As a result, there is a fear that the replenishing characteristic of liquid is deteriorated, because the valve is allowed to cut off the liquid flow path again before refilling has been carried out sufficiently.
Also, in the same specification, the disclose valve mechanism is such that the valve member is structured so as to form a hole on the center thereof to release the central part of the liquid flow path in the steady state. With this structure, however, the pressure exerted by driving the heat generating member is allowed to escape to the common liquid chamber side during the period until the deformed valve member is closely in contact with the valve seat, thus inevitably making the effect smaller in enhancing the energy efficiency.
Further, in the same specification, the disclosed structure is such that another passage is arranged to detour around the liquid flow path provided for the valve mechanism, but with the structure thus arranged, the pressure exerted by driving the heat generating member is partly allowed to escape through this passage, thus making the effect smaller in enhancing the energy efficiency. Also, the difference of pressures across the valve member that deforms the valve member is eased by way of this passage to make it impossible to effectuate the displacement of the valve member sufficiently. As a result, there is a fear that function of the valve mechanism is degraded eventually.
Now, therefore, it is an object of the present invention to provide an ink jet recording head provided with a novel valve mechanism whereby to solve the problems existing in the conventional examples discussed above by effectively utilizing the structural characteristics in the flow path so that not only the energy efficiency is enhanced, but the refilling of liquid can be executed smoothly.
From the different point of view, the present invention aims to provide an ink jet recording head having the movable member which is capable of efficiently regulating each bubble to be formed by film boiling with the substantial upper limit defined in the height component from the surface of a bubble to be generated (the surface of the heat generating member) depending on the height of the flow path for the bubble which is formed by film boiling generated in liquid by means of electrothermal converting device (heat generating member).
In order to solve the problems discussed above, the liquid discharge head of the present invention comprises discharge ports for discharging liquid as droplets; liquid flow paths communicated with the discharge ports, being provided with heat generating members for generating bubbles by providing thermal energy for liquid; and a common liquid chamber for retaining liquid to be supplied to the liquid flow paths. For the liquid discharge head thus structured, a narrower portion is provided between the liquid flow path and the heat generating member, and between the narrower portion and the heat generating member, a displaceable plate type movable member is provided in the liquid flow path thereof, and this movable member is formed to stand up from the surface of the liquid flow path having the heat generating member in the direction substantially perpendicular to the liquid supplying direction, having a designated gap in the narrower portion in the liquid supplying direction, and a fine gap in the plane of the free end thereof facing the surface of the liquid flow path having the heat generating member.
With the structure thus arranged, when a pressure is exerted by the bubble generated by the heat generating member, the movable member is displaced to the narrower portion side by the pressure thus exerted to close the liquid flow path substantially. Thus, the movement of liquid is prevented from shifting to the common liquid chamber side (upstream side) which is the side opposite to the discharge port of the liquid flow path. In this manner, the diffusion of the pressure exerted by bubbling to the upstream side is suppressed so as to conduct the exerted pressure to the discharge port side (downstream side) efficiently. Particularly, in the initial stage of bubbling, the bubble tends to be stretched horizontally in the vicinity of the plane (lower face) where the heat generating member is provided. However, with the movable member which is formed to stand up from the lower face, it becomes possible to effectively close around the lower face by means of the movable member, thus reducing the diffusion of the pressure waves in the upstream direction significantly when generated by the bubble in the initial stage of bubbling.
Also, when the bubble is grown, liquid cannot move in the plane (ceiling) direction that faces the surface where the movable member and the liquid flow path are formed. As a result, the bubble tends to be stretched mainly in the horizontal direction, and can hardly reach the ceiling. Then, in the vicinity of the ceiling, a fine layer (approximately 10 xcexcm) is formed where almost no liquid flows. Further, since the pressure is propagated from the bubble to the liquid mainly on the normal line direction of the surface of the bubble, there is almost no flow of liquid in the liquid flow direction on this layer. Then, it is made easier for the liquid to flow gradually from this layer to the central portion of the flow path. For the present invention, it is desirable to set the height of the movable member that forms the fine gap in the ceiling at the height where the area of liquid flowing largely in the liquid flow path direction, that is, at the lower limit of the height of bubble when the bubble is grown to the maximum in the process of discharging liquid. Then, it is desirable to define the upper limit of the height of movable member so that this fine gap can secure the sufficient height to enable the aforesaid layer to be located therein with almost no liquid flow on the layer. With the fine gap thus set between the movable member and the ceiling, it becomes possible for the movable member to substantially close the area in the height direction, in which a large flow of liquid may occur in the liquid flow path direction if the movable member is not present. As a result, there is almost no diffusion of liquid to the upstream side through the fine gap during the growing process of the bubble. (There may be present, however, the liquid flow that passes the side direction of the movable member.)
On the other hand, by the exertion of the force after liquid is discharge, which causes liquid to flow to the heat generating member side due to the lowered pressure resulting from debubbling, the movable member is warped and deformed to the heat generating member side, and the gap between the movable member and the ceiling becomes larger. The free end of the movable member comes to the lower position, thus releasing partially the area where a large liquid flow may take place in the liquid flow direction to make it possible to induce liquid efficiently from the common liquid chamber into the liquid flow path.
In this way, the ink jet recording head of the present invention can suppress the diffusion of liquid to the upstream side when the heat generating member exerts pressure by bubbling, and induce liquid into the liquid flow path efficiently after liquid is discharged. Therefore, in the entire processes of liquid discharge, liquid can move from the common liquid chamber side to the discharge port side effectively, thus enabling the time to be shortened, which is required for filling liquid in the liquid flow path after ink has been discharged.
As described earlier, the area where almost no liquid flow occurs in the liquid flow path direction is an area within a distance of approximately 10 xcexcm from the ceiling. It is desirable to set the fine gap between the movable member and the ceiling at 2 xcexcm or more and 15 xcexcm or less in condition that the movable member is not allowed to be deformed. Also, it is desirable to set the distance at 10 xcexcm or less between the movable member and the narrower portion in the liquid flow path direction in order not to allow the fine gap to becomes excessive when the movable member is displaced to the narrower portion side.
Also, if the heat generating member is driven for a long time, the conventional head accumulates heat to cause the inner temperature of the ink jet recording head to rise high. In this case, the bubble grows larger with the same driving energy given to the head as compared with the case where the temperature is low. As a result, the amount of liquid discharges is caused to change eventually. For the ink jet recording head of the present invention, efficiency is improved as described above so that the area of the heat generating member is made smaller in order to provide the same amount of liquid discharge at the same discharge speed as the conventional one. In other words, it becomes possible to make the driving energy smaller than the one needed for the conventional ink recording head, hence suppressing and keeping the increase of the amount of liquid discharge to be small.
For the ink jet recording head of the present invention, it is desirable to set a distance at 30 xcexcm or less between the movable member and the end portion of the heat generating member on the movable member side and the movable member, because otherwise the effect to suppress the diffusion of pressure to the upstream side becomes unsatisfactory due to the loss of the spacial energy when the bubble grows, and also, because the effect to deform the movable member to the heat generating member side becomes unsatisfactory when the bubble enters the process of debubbling.
As the material of the movable member, it is possible to use either silicon nitride, silicon oxide, or silicon carbide.
Also, from the different point of view, the features of the liquid discharge head of the present invention are such that the aforesaid movable member is made displaceable without being in contact with the plane of the liquid flow path that faces the surface where the heat generating member is provided, and the height of the movable member in the substantially perpendicular direction is higher than that of the bubble in the substantially perpendicular direction during the period from the generation of film boiling in liquid by the heat generating member to the maximum growth of the bubble formed by this film boiling. With the movable member thus provided, this member acts as the fluid resistive element to the pressure waves and liquid flow that runs, along with the growth of the bubble, to the backside region (refilling side) which is opposite to the discharge port, while the movable member is deformed or displaced at the time of refilling, thus making it possible to enhance the refilling effect.
In manufacturing the liquid discharge head of the present invention, the side walls of the liquid flow path and the movable member can be simultaneously formed by means of the semiconductor manufacturing process. This simultaneous formation of the liquid flow path walls and movable member promotes the efficiency of manufacturing. Also, in such semiconductor manufacturing process, structures of different configurations can be formed with ease on one and the same manufacturing line simply by changing mask patterns for etching or the like, thus making it easier to manufacture an ink jet recording head having the liquid flow path walls and movable member in different configurations. Here, also, the liquid flow path walls are formed by means of the semiconductor manufacturing process which is used for forming the heat generating members and driving circuit on a base plate, hence making the manufacture of a liquid discharge head possible with these members having high dimensional precision.
Also, the liquid discharge apparatus of the present invention is provided with the aforesaid liquid discharge head mounted thereon to enable droplets to adhere to a recording medium. This apparatus comprises a mechanism for carrying a recording medium.
In this respect, the description in the specification hereof to the effect that the xe2x80x9cmovable member stands up in the direction substantially perpendicular to the liquid supplying directionxe2x80x9d means that the inclination of the movable member in the direction in which it stands up is within a range of approximately 10xc2x0 in the direction perpendicular to the liquid supply direction.
Also, in the specification hereof, the xe2x80x9csurface where the heat generating member is providedxe2x80x9d is meant to include the face becoming the base of a heat generating member, the surface of the heat generating member, the surface of the protection layer to protect the heat generating member, and the like, which exist on the upper layer and lower layer of the plane where the heat generating member is provided, and the value of layer thickness of which is essentially negligible in comparison with the value of the height of the movable member.